That’s where Uber had set up a pick-up lounge for DNC attendees not fortunate enough to have a designated delegate bus or hotel within walking distance of a Philadelphia subway stop.

“We had our busiest day ever in Philadelphia,” said Niki Christoff, head of the company’s federal affairs group, who said that official ride numbers won’t be available until the convention ends.

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Uber’s partnership with the DNC began early this year, when the ride-hailing giant visited both the Democratic and Republican National Committees in Washington, D.C. It offered both parties the following deal: Uber would provide a dedicated fleet of complimentary vehicles to ferry VIPs (e.g., speakers, certain delegates, etc.) around the convention cities. In exchange, the party would provide Uber with an exclusive car lot inside the outer security perimeter.

The RNC turned down the deal, leading Uber to rent out a private “lounge” space outside of the Cleveland security perimeter. The DNC ― whose convention is located seven miles outside of Philadelphia’s city center ― said yes.

For Uber, however, the agreement presented some personnel challenges. Namely, how would it convince enough drivers to hang out in a traffic-infested parking lot rather than roaming the streets.

The solution was financial incentives. Specifically, all Uber drivers who pick up riders at during the DNC are guaranteed minimum earnings of between $21 and $27 per hour (depending on the time period). If actual earnings comes in below that amount, Uber picks up the difference.

There had been some social media rumors that Uber was penalizing Philadelphia-area drivers who declined to drive during the convention, but multiple drivers tell Fortune that is not the case, and company officials have publicly denied the allegations.